The overall goal of this project is to generate antibody-modified adenoviral vectors for cell/tissue specific gene delivery. Adenovirus-based vectors are widely used for gene delivery and gene therapy clinical trials. These vectors are advantageous in that they can be prepared to high titers with high purity and can deliver gene to a variety of cell types. The low tissue specificity of Ad-based vectors has restricted the potential application of these vectors as a treatment for acute and chronic diseases. Ad infection is initiated by high affinity interaction of viral fiber protein with its cellular receptor CAR (coxsackie adenovirus receptor). Modification of the fiber protein (the determinant for virus tropism) has been a major strategy to improve gene delivery specificity. Ad fiber is a homotrimeric protein that contains an N-terminal tail, responsible for its non-covalent attachment to virus surface, a shaft region, and a C-terminal knob, essential for cell surface attachment. The trimerization domain was proposed to be in the knob region of the C-terminus. Thus, fiber modification to improve tissue specificity has mainly focused on this region, although such modification tends to disrupt fiber trimer, resulting in the assembly of incomplete virions. This proposal focuses on the modification of Ad vectors by fusing cell specific ligands such as antibodies to the N-terminal shaft of Ad fiber protein. Three specific aims are proposed to address the design and gene delivery efficiency of these vectors. AIM 1. To develop reporter Ad vectors by replacing fiber protein with chimeric TEF-tumor targeting single chain antibody. AIM 2. To determine gene delivery selectivity in in vivo tumor models by measuring reporter gene expression in tumor and organs. AIM 3. To construct and to determine the efficacy of therapeutic genes delivered by antibody-modified vectors by measuring tumor growth in colorectal tumor murine transgenic models. The new Ad vectors would have combined advantages of high delivery efficiency (by Ad) and high tissue specificity (by antibodies).